Chapter 19 The Brain and Cranial Nerves

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Chapter 19The Brain and Cranial Nerves

• Brain functions in sensations, memory, emotions,
  decision making, behavior

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Principal Parts of the Brain

• Cerebrum
• Diencephalon
• thalamus hypothalamus
• Cerebellum
• Brainstem
• medulla, pons midbrain

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Protective Coverings of the Brain

• Bone, meninges fluid
• Meninges same as around the spinal cord
• dura mater
• arachnoid mater
• pia mater

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Blood Supply to Brain

• Arterial blood supply is branches from circle of
  Willis on base of brain 99)
• Vessels on surface of brain----penetrate tissue
• Uses 20 of our bodies oxygen glucose needs
• blood flow to an area increases with activity in
  that area
• deprivation of O2 for 4 min does permanent injury
• at that time, lysosome release enzymes
• Blood-brain barrier (BBB)
• protects cells from some toxins and pathogens
• proteins antibiotics can not pass but alcohol
  anesthetics do
• tight junctions seal together epithelial cells,
  continuous basement membrane, astrocyte processes
  covering capillaries

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Cerebrospinal Fluid (CSF)

• 80-150 ml (3-5oz)
• Clear liquid containing glucose, proteins, ions
• Functions
• mechanical protection
• floats brain softens impact with bony walls
• chemical protection
• optimal ionic concentrations for action
  potentials
• circulation
• nutrients and waste products to and from
  bloodstream

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Origin of CSF

• Choroid plexus capillaries covered by
  ependymal cells
• 2 lateral ventricles, one within each cerebral
  hemisphere
• roof of 3rd ventricle
• fourth ventricle

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Drainage of CSF from Ventricles

• One median aperture two lateral apertures allow
  CSF to exit from the interior of the brain

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Flow of Cerebrospinal Fluid
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Reabsorption of CSF

• Reabsorbed through arachnoid villi
• grapelike clusters of arachnoid penetrate dural
  venous sinus
• 20 ml/hour reabsorption rate same as production
  rate

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Medulla Oblongata

• Continuation of spinal cord
• Ascending sensory tracts
• Descending motor tracts
• Nuclei of 5 cranial nerves
• Cardiovascular center
• force rate of heart beat
• diameter of blood vessels
• Respiratory center
• medullary rhythmicity area sets basic rhythm of
  breathing
• Information in out of cerebellum
• Reflex centers for coughing, sneezing, swallowing
  etc

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Ventral Surface of Medulla Oblongata
Olive olivary nucleus neurons send input to
cerebellum proprioceptive signals gives precision
to movements

• Ventral surface bulge
• large motor tract
• pyramids
• left cortex controls right muscles

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Dorsal Surface of Medulla Oblongata

• Nucleus gracilis nucleus cuneatus sensory
  neurons
• relay information to thalamus on opposite side of
  brain
• 5 cranial nerves arise from medulla -- 8 thru 12

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Injury to the Medulla

• Hard blow to the back of the head may be fatal
• Cranial nerve malfunctions on same side as
  injuryloss of sensation or paralysis of throat
  or tongue irregularities in breathing and heart
  rhythm

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Pons

• One inch long
• White fiber tracts ascend and descend
• Pneumotaxic apneustic areas help control
  breathing
• Middle cerebellar peduncles carry sensory info to
  the cerebellum
• Cranial nerves 5 thru 7

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Midbrain

• One inch in length
• Extends from pons to diencephalon
• Cerebral aqueduct connects 3rd ventricle above to
  4th ventricle below

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Midbrain in Section

• Cerebral peduncles---clusters of motor sensory
  fibers
• Substantia nigra---helps controls subconscious
  muscle activity
• Red nucleus-- rich blood supply iron-containing
  pigment
• cortex cerebellum coordinate muscular movements
  by sending information here from the cortex and
  cerebellum

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Cerebellum

• 2 cerebellar hemispheres and vermis (central
  area)
• Function
• correct voluntary muscle contraction and posture
  based on sensory data from body about actual
  movements
• sense of equilibrium

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Cerebellum

• Transverse fissure between cerebellum cerebrum
• Cerebellar cortex (folia) central nuclei are
  grey matter
• Arbor vitae tree of life white matter

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Cerebellar Peduncles

• Superior, middle inferior peduncles attach to
  brainstem
• inferior carries sensory information from spinal
  cord
• middle carries sensory fibers from cerebral
  cortex basal ganglia
• superior carries motor fibers that extend to
  motor control areas

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Diencephalon Surrounds 3rd Ventricle

• Surrounds 3rd ventricle
• Superior part of walls is thalamus
• Inferior part of walls floor is hypothalamus

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Thalamus

• 1 inch long mass of gray mater in each half of
  brain (connected across the 3rd ventricle by
  intermediate mass)
• Relay station for sensory information on way to
  cortex
• Crude perception of some sensations

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Thalamic Nuclei

• Nuclei have different roles
• relays auditory and visual impulses, taste and
  somatic sensations
• receives impulses from cerebellum or basal
  ganglia
• anterior nucleus concerned with emotions, memory
  and acquisition of knowledge (cognition)

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Hypothalamus

• Dozen or so nuclei in 4 major regions
• mammillary bodies are relay station for olfactory
  reflexesinfundibulum suspends the pituitary
  gland
• Major regulator of homeostasis
• receives somatic and visceral input, taste, smell
  hearing information monitors osmotic pressure,
  temperature of blood

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Functions of Hypothalamus

• Controls and integrates activities of the ANS
  which regulates smooth, cardiac muscle and glands
• Synthesizes regulatory hormones that control the
  anterior pituitary
• Contains cell bodies of axons that end in
  posterior pituitary where they secrete hormones
• Regulates rage, aggression, pain, pleasure
  arousal
• Feeding, thirst satiety centers
• Controls body temperature
• Regulates daily patterns of sleep

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Reticular Formation

• Scattered nuclei in medulla, pons midbrain
• Reticular activating system
• alerts cerebral cortex to sensory signals (sound
  of alarm, flash light, smoke or intruder) to
  awaken from sleep
• maintains consciousness helps keep you awake
  with stimuli from ears, eyes, skin and muscles
• Motor function is involvement with maintaining
  muscle tone

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Cerebrum (Cerebral Hemispheres)

• Cerebral cortex is gray matteroverlying white
  matter
• 2-4 mm thick containing billionsof cells
• grew so quickly formed folds(gyri) and grooves
  (sulci or fissures)
• Longitudinal fissure separates left right
  cerebral hemispheres
• Corpus callosum is band of white matter
  connecting left and right cerebral hemispheres
• Each hemisphere is subdivided into 4 lobes

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Lobes and Fissures

• Longitudinal fissure (green)
• Frontal lobe
• Central sulcus (yellow)
• precentral postcentral gyrus
• Parietal lobe
• Parieto-occipital sulcus
• Occipital lobe
• Lateral sulcus (blue)
• Temporal lobe
• Insula

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Insula within Lateral Fissure
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Cerebral White Matter

• Association fibers between gyri in same
  hemisphere
• Commissural fibers from one hemisphere to other
• Projection fibers form descending ascending
  tracts

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Basal Ganglia

• Connections to red nucleus, substantia nigra
  subthalamus
• Input output with cerebral cortex, thalamus
  hypothalamus
• Control large automatic movements of skeletal
  muscles

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Limbic System

• Emotional brain--intense pleasure intense pain
• Strong emotions increase efficiency of memory

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Functional organization of the cerebral cortex
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Sensory Areas of Cerebral Cortex

• Receive sensory information from the thalamus
• Primary somatosensory area postcentral gyrus
  1,2,3
• Primary visual area 17
• Primary auditory area 41 42
• Primary gustatory area 43

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Motor Areas of Cerebral Cortex

• Voluntary motor initiation
• Primary motor area 4 precentral gyrus
• controls voluntary contractions of skeletal
  muscles on other side
• Motor speech area 44 Brocas area
• production of speech -- control of tongue airway

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Association Areas of Cerebral Cortex

• Somatosensory area 5 7 (integrate
  interpret)
• Visual association area 18 19 (recognize
  evaluate)
• Auditory association area(Wernickes) 22(words
  become speech)
• Gnostic area 5,7,39 40 (integrate all senses
  respond)
• Premotor area 6 (learned skilled movements such
  as typing)
• Frontal eye field 8 (scanning eye movements such
  as phone book)

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Hemispheric Lateralization

• Functional specialization of each hemisphere more
  pronounced in men
• Females have larger connections between 2 sides
• Damage to left side produces aphasia
• Damage to same area on right side produces speech
  with little emotional inflection

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I -- Olfactory Nerve
Cranial Nerves

• Extends from olfactory mucosa of nasal cavity to
  olfactory bulb
• Sense of smell

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II -- Optic Nerve

• Connects to retina supplying vision

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III Oculomotor Nerve

• Levator palpebrae raises eyelid (ptosis)
• 4 extrinsic eye muscles
• 2 intrinsic eye muscles
• accomodation for near vision (changing shape of
  lens during reading)
• constriction of pupil

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IV Trochlear Nerve

• Superior oblique eye muscle

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V Trigeminal Nerve

• Motor portion
• muscles of mastication
• Sensory portion
• touch, pain, temperature receptors of the face
• ophthalmic branch
• maxillary branch
• mandibular branch

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VI Abducens Nerve

• Lateral rectus eye muscle

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VII Facial Nerve

• Motor portion
• facial muscles
• salivary nasal and oral mucous glands tears
• Sensory portion
• taste buds on anterior 2/3s of tongue

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VIII Vestibulocochlear Nerve

• Cochlear branch begins in medulla
• receptors in cochlea
• hearing
• if damaged deafness or tinnitus (ringing) is
  produced
• Vestibular branch begins in pons
• receptors in vestibular apparatus
• sense of balance
• vertigo (feeling of rotation)
• ataxia (lack of coordination)

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IX Glossopharyngeal Nerve

• Stylopharyngeus m. (lifts throat during
  swallowing)
• Secretions of parotid gland
• Somatic sensations taste on posterior 1/3 of
  tongue

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X Vagus Nerve

• Receives sensations from viscera
• Controls cardiac muscle and smooth muscle of the
  viscera
• Controls secretion of digestive fluids

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XI Spinal Accessory Nerve

• Cranial portion
• arises medulla
• skeletal mm of throat soft palate
• Spinal portion
• arises cervical spinal cord
• sternocleidomastoid and trapezius mm.

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XII Hypoglossal Nerve

• Controls muscles of tongue during speech and
  swallowing
• Injury deviates tongue to injured side when
  protruded
• Mixed, primarily motor